Process for heat treating silicon steel sheets



Patented Feb. 12, 1935 UNITED STATES PROCESS FOR HEAT TREATING SILICON STEEL SHEETS William E. Caugherty, Natrona, Pa., assignor to Allegheny Steel Company, a corporation of Pennsylvania No Drawing. Application September 26, 1929, se'lal No. 395,465. Renewed February 2'1,

14 Claims. (01. lie-21.5)

This invention relates to silicon steel sheets such as used in the construction of certain parts of electrical apparatus, and comprises a method of treating such sheets whereby their magnetic 5 properties and physical characteristics are improved.

In an application filed jointly by Carl J. Stroble and me on June 30, 1927, which application matured into Patent No. 1,706,438, there is set forth notonly a method new with us at that time of treating silicon steel sheets to-improve their quality, but also various methods theretofore practiced in the treating of such sheets.

While results are possible of attainment-which are superior to those methods in vogue at the time of flling said application--by the method of said Patent No. 1,706,438, it is nevertheless a fact that sheets treated or annealed in the manner therein set forth are not as flat as box annealed sheets and in addition they have the disadvantage of having a fairly heavy marginal scale. This lack of flatness prevents sheets annealed in accordance with the method of said patent from being used for electrical apparatus of large size such as power transformers, because with sheets lacking in proper flatness, laminations produced therefrom will not stack properly. The presence of the marginal scale is a seriousv disadvantage to users who punch laminations from such sheets as the scale causes excessive wear on the punching dies. The scale is also a disadvantage when the sheets are to be used in transformers operating at high inductions since, due to the scale, less active steel can be placed in a given space, thereby rendering a higher magnetizing force necessary for a given flux.

An object of this invention is to provide a new method of treating silicon steel sheets for improvingtheir magnetic properties.

' Another object of this invention is to provide a method of so treating silicon steel sheets that their magnetic values as well as their physical characteristics are improved.

A still further object of this invention is to 9 provide a method for the treatment of silicon 7 steel sheets whereby (without the use of elaborate and costly equipment, such as is necessary for obtaining a high temperature hydrogen anneal) the maximum values for use in electrical appa- 80 ratus may be obtained from a given batch of sheets of silicon steel.

Broadly, my invention consists in normalizing oropenannealingsiliconsteelsheetsandthen stackormassannealingasinboxannealing' More specifically, my invention which is applicable to the treating of silicon steel sheets which have been rolled by any standard or suitable method (generally hot rolled in accordance normalizing or open annealing the sheets at a temperatureof from about 1500 F. to about 1800? F. either singly or in packs of four or more; allowing suflicient time for the sheets to attain the temperature required; and, in box annealing the sheets at a furnace temperature of about 1500 F.

In the step of box annealing, where a relatively large number of sheets constituting a stack are placed in an annealing box which is moved into a suitable furnace, the temperature of the stacks of sheets is gradually built up until the desired temperature is attained; this temperature is then maintained for a considerable period of time and then the temperature of the stack of sheets is allowed to gradually drop.

I have found that by utilizing a furnace temperature of about 1500 F., I can obtain a sheet temperature or a temperature of the stack of sheets which is suflicient to prevent aging and I have found that it is preferable as I have said, to gradually raise thetemperature of the stack of sheets until it reaches the annealing temperature, to hold the stack at that temperature for a considerable period of time and then to gradually lower the temperature from annealing temperature. I have found that satisfactory results can be obtained by taking one and one-half times as long to build up the temperature of the stack to annealing temperature as is utilized for holding the stack at annealing temperature and then in taking from seven to eight times as long in cooling the stack down from annealing temperature as is utilized in holding the stack at annealing temperature. This annealing cycle will depend somewhat upon the gauge of the sheets being treated and the weight of the stack-or of sheets.

There are two main reasons for following the open anneal or normalizing step by a box anneal. The first, as already pointed out, is to flatten the sheets which have become slightly warped by rapid cooling after the normalizing or open anneal step. The second, and probably most important, is to render the sheet-non-aging. It

has been discovered that silicon steel sheets which have been normalised or open annealed only, will, when subjected to a temperature of about 200 F., even for a short period of time, show an increase in hysteresis loss-or will, as it is commonly us the sheets, heating the In the normalizing or open annealing step according to my method, I do not limit myself to temperatures of about 1800 1"., since I have found that good results may be obtained at somewhat ldwer temperatures. I prefer the higher temperatures, however, for the reason that the results desired can be obtained in a shorter period of time, than with lower temperatures. I have determined that by annealing at about 1800 F., the desired results can be obtained in about oneninth the time, a comparable result can be obtained if annealing occurs at about 1500 F.

I do not limit nu! normalizing or open annealing step to any particular type of furnace. but I prefer a continuous type either table roller driven or endless wire rope driven.

While it has been steel sheets at a an increase in grain size current losses, I have found are held at such temperatures for but a short time and are then cooled rapidly,

about 1000' P. and merely held at this temperature long enough to become thoroughly heated to such temperature throughout and are then cooled rapidly and then immediately box annealed at a furnace temperature of about 1500 F. have elecor annealed in any other manner known to me.

WhatIclaimasnewanddesh-etos'ecureby Letters Patent is:-

1. A method for treating hot rolled silicon steel sheets, which includes the steps of pickling sheets completely to about 1800 1". and then box annealing the sheets.

2. The method of preparing silicon steel sheets for electrical purposes which includes the steps or hot rolling and pickling the sheets, heating them to 1500-1800 F., rapidly cooling, and then box annealing them.

3. A method of preparing silicon steel for use in electrical apparatus, which includes the steps of rolling suitable silicon steel to sheet-like form,

inheatingtherolledmaterialcompletelytoirom' about 1500 F. to 1800 R, in quickly cooling the same and then in box annealing the material.

6. A method 01' like form to render the same non-aging comprising the consecutive steps of open annealing and then box annealing the material.

7. A method of treating silicon steel in sheetlike form to flatten and render the same nonaging, which consists in open annealing at from about 1500 to about 1800 F. and in then box annealing the same.

8. A method of improving the magnetic properties of silicon steel in sheet-like form, which consists in pickling the material, in normalizing the pickled material, in annealing such material to remove cooling strains and then in slowly cooling the material.

9. A method of treating rolled silicon steel in sheet-1ike form, which consists in pickling the sheet-like material, in open annealing said material at about 1800 in cooling said material rapidly, in box annealing said material at a furnace temperature or about 1580 F. and then in slowly cooling the same.

10. A method of treating silicon steel in sheetlike form to render the same non-aging, consisting in open annealing at about 1800 R, in then box annealing at a temperature sufllcient to impart to the material a temperature of at least 1400 F. and then in slowly cooling.

11. A method of treating silicon steel for use in electrical apparatus, which consists in rolling suitable silicon steel to sheet-like form, in open annealing the rolled material at a tempera- Lure of from 1500" to 1800 F. and then in box annealing the same.

12. A method of treating silicon steel for use in electrical apparatus, which consists in rolling suitable silicon steel to sheet-like form, in open annealing the rolled material at a temperature of at least 1800 F. and then in box annealing the same.

13. A method of treating silicon steel for use in electrical apparatus, which consists in rolling suitable silicon steel to sheet like form, in open annealing the rolled material at a temperature of from 1500 to 1800 F., in quickly cooling the material, then in slowly raising the same to annealing temperature, in holding the same at such temperature for a time sufllcient to prevent aging and then in slowly cooling the same.

14. A method of inhibiting aging in silicon steel for use in electrical apparatus comprising reducing such silicon steel to sheet-like form, open annealing it at about 1800' 1"., and, without intermediate treatment but permitting cooling annealing the same at a furnace flcient to impart to the WILLIAM E, CAUGHSR'I'Y.

treating silicon steel in sheet-, 

